Airline regulations are likely to be a problem here. As a general rule, they don't allow this. Your customer is unlikely to get flagged, but if he is flagged, he'll at the very least have to re-buy the same ticket with his own card, and at worst may not be able to board.
You say that you are new to the services, so you're not really experienced with how the compensation system works. There are ways this could blow up badly for you - not least, you book the ticket, they fly, then they dispute or cancel the work, or claim you did not perform adequately. You now eat the cost of the airline ticket. That forks into several options:
- The customer paid you via the platform, in which case it gets reversed and you are left holding the bag.
- You circumvent the platform to contact the customer privately, and he pays you in some third-party manner. Your first problem is you have violated the platform's TOS. Which means if this blows up into an issue, you won't be on the platform anymore. The customer can use this to intimidate you. But then --
- If the private payment method is reversible, they can reverse it and you are left holding the bag. You have no recourse through the platform.
These online work platforms are also magnets for scammers. That is, they want to get free/cheap airline tickets or stuff, and they are looking for ways to use the platform to get people to buy them things, and then, reneg on payment. So if there's a way that's possible on the platform, they will have found it.
That begs the question of why do you want to buy airline tickets for customers on those platforms?. I don't imagine you just dreamed this up. I'd imagine that you you have connected with customers on the platform who are asking you to do this. Obviously you think they are legit, but hold on -- you are surely violating the platform's Terms of Service*, which means, so are they. Normal customers don't do that.
So yeah, this sounds like you are involved in a confidence game.